Not necessarily. There are a lot of dynamics (mechanically and thermally) going on in an engine. Clearances can be very tight and only under certain conditions might a valve make contact with the piston. And light valve contact isn't always immediately catastrophic. Jhoffy makes reference to a noise he thought was pinging...could have been light contact going on all along. The final failure could have been due to a fatigued valve stem from light contact, or it could have been due to heavy contact at the right dynamic condition in the engine.

...Or it could have been something else.

 

Would you call shifting without letting off the gas the right dynamic condition? This combined with the changed valve clearance of the cam timing mod could have done me in...

 

Lutz - true, could very well have been tapping all along, then it just had too much and boooom.

 

you mentioned that the bike was modded when you got it, aftermarket pipe anyway. did you know the previous owner,and how the bike was treated before you got it? did the bike look clean or did it look pretty well abused? do you think maybe the PO beat on the bike to the extent that the valves were already out of spec prior to you fussing with it? Could be that that exhaust valve was already toast and you didn't catch it in the rebuild since you didn't figure on the bike having an issue already. just food for thought. Get another piston and rings if the cylinder checks out OK. If the cylinder is not damaged, and the cross hatch is still good, your new rings will seat without a problem. you only have a few miles on the hone so that is not an issue. if you have the paperwork bill sent with the piston and rings it will have the bore size listed so Bill can file fit the rings again for you without having the cylinder. Call him up and tell him what happened so he knows what you need. BTW he might have a head too. when you do get a head be sure you get new valve springs.DO NOT USE THOSE.
Good luck and keep the faith, could have been worse,,, much worse.

 

do you still have the stock barrel and piston?

 

Are you saying that you pull in the clutch, shift, release clutch WITHOUT letting off the throttle???? Even with new valve springs, that would be a good way to float the valves!!!!!!!!! From what I've been reading, the engine has the original valve springs.
That could very well be what caused the grenade.

Ride on
Brewster

 

I missed this part, no doubt winding it up to near red line and feathering the clutch is gonna do bad things.

 

Yeah, from what I could tell everything was stock. Judging by the wiring job under the seat and the pics I posted in the other thread, they didn't really know what they were doing. The chain case saver and sprocket guard were both missing. If my chain breaks, it's going through the crank case. I don't think they took the best care of it, but everything was pretty sound when I got it. I was stupid for not inspecting the valves when I got the bike. I need to look at a diagram of the cylinder head to compile a list of all the components that I need to order. I'm not sure how to effectively inspect the cylinder to make sure that it will be okay for a new piston, what is the cross hatch? I emailed Bill but I'm going to give him a call tomorrow and see if he can sell just the piston and rings. I feel bad bothering him all the time. That would be awesome if he had a head too. I'm looking for someone that does ported heads right now. I just hope this problem doesn't reoccur. That's what scares me the most, is not being able to diagnose the problem 100% and have the possibility of it happening again and ruining all of the new parts. So for the head, I'll need the valves, shims, tappets and valve springs. Is there anything else there?

I'm not sure if they are the original valve springs or not, but yes I did exactly that. I know other people that drive like that, and they tell me that it is best to get stiffened springs. I didn't think doing it once would hurt anything.

 

I GOT IT ! Okay, it was not the 351 kit, it was not the cam mod. I do this kind of work all the time, I'm Team Green certified and after looking at all these pics, I'd say you broke a valve, nothing more, certainly nothing less. Parts break. I don't know Jhoffy's mechanical ability, but, man you got some stones. The cam mod is not what I'd call "backyard" stuff. Don't over analyze, the valve broke. Valves break, new ones break, old ones break, just sucks that yours broke.

 

Thanks for the compliment! Maybe the valves were crappy to begin with but I still think the combo of the 351 and the cam mod were contributing factors. But I will take your word for it and start everything over again. Any insider information on a good place to get a new ported polished head?